Combination transformer and buzzer device



Feb. 15, 1966 F. M. WESLEY COMBINATION TRANSFORMER AND BUZZER DEVICE Film 7, 1962 E re? Freak M /e) .around another portion thereof.

United States Patent 3,235,864 COMBINATION TRANSFORMER AND BUZZER DEVICE Frank M. Wesley, Palos Park, Ill., assignor to Stewart- Warner Corporation, Chicago, 111., a corporation of Virginia Filed Aug. 17, 1962, Ser. No. 217,710 5 Claims. (Cl. 340-384) This invention relates to a device for indicating an alarm condition. More particularly, this invention relates to a device which operates as a transformer and a buzzer, it being an improvement over a device disclosed and claimed in the copending application of Marshall Miles, Serial No. 161,686, filed December 22, 1961, entitled Temperature Indicating Device.

The device of this invention has been developed for use in temperature indicating systems for use with cooking stoves or the like. -Although the device has obvious application to many other fields, it will be described herein in relation to such a temperature indicating system.

Generally, in these systems the transformer provides a low voltage current from the normal house supply which is conducted through a bi-metal heater coil so that the heat produced thereby at the desired temperature condition deflects the bi-metal to close contacts and energize an alarm device. The circuits usually include a bi-rnetal heating coil connected in series with a thermistor, or other heat sensitive device, across the low voltage .winding of the transformer. Thus the amount of current through the bi-unetal heating coil is dependent on the temperature of the thermistor.

In the aforementioned Miles application, there was shown a device for performing the functions of both a transformer and an alarm which materially reduced the cost-s of a temperature indicating system. That device included a closed loop core with a primary winding around one portion of the core and a secondary winding A magnetic flux permeable vibrating element extended across the core between the two windings .to provide the alarm buzzer function. In that device the :vibrating element is energized responsive to short circu-iting of the secondary winding which causes high flux concentration through the portion of the core surrounded by the secondary winding. Thus, magnetic flux flows through the auxiliary path provided by the vibrating element causing it to vibrate responsive to the 60 cycle fluctuations of the house current supply.

The device as briefly described and disclosed more fully in the Miles application required specially designed components throughout due to the closed loop shape of the core. It also required diflicult and expensive assembly techniques, especially in the winding of the primary and secondary coils because of the loop design of the core.

It is, therefore, an object of this invention to provide a device operable as both a transformer and an alarm buzzer.

It is also an object of this invention to provide a device which operates as both an electrical transformer and an alarm buzzer which is constructed of inexpensive components and is readily adapted for easy assembly in mass production.

Another object of this invention is to provide a device operable as both an electrical transformer and an alarm buzzer which comprises a transformer core of standard design.

Other objects and advantages of this invention will become readily apparent upon further reading of this specification especially when taken in view of the accompanying drawings, in which:

FIG. 1 is an isometric view of the device of this inven- 3,235,864 Patented Feb. 15, 1966 tion as connected in a schematic-ally simplified temperature indicating system;

FIG. 2 is an isometric view of the transformer core showing the coils and the buzzer mechanism in phantom to indicate the flux paths during normal low load operation; and

FIG. 3 is an isometric view partially broken away showing the details of construction and the flux paths therethrough under high load conditions.

Briefly, the device of this invention comprises a shelltype core having a loop portion and a center leg with a primary winding and a secondary winding surrounding the center leg. A bracket supporting a vibratable element is secured to the center leg portion of the core to provide an auxiliary flux path through the vibratable element.

Describing the invention more fully, a preferred embodiment of the transformer buzzer device 10 comprises a standard shell-type core as shown best in FIG. '3. The shell-type core comprises a loop portion 14 with a center leg 16 extending across the loop. The core is made up of alternately positioned E-shaped and I-shaped laminations in the standard manner to reduce eddy currents.

A primary winding 18 surrounds one portion of the center leg 16 and a secondary winding 20 surrounds another portion of the center leg, both windings being contained within the loop portion 14. A U-shaped bracket 22 having an aperture 24 in its base portion 26 is supported by the center leg 16 received by the aperture .24 between the primary and secondary windings. The bracket 22 is fabricated of magnetic flux permeable material and is connected at the aperture to the center leg 16 so as to provide an alternate magnetic flux path as hereinafter described. The leg portions 28 and 30 of the U-shaped bracket 22 extend around the secondary winding 20 and each terminate at a point just beyond the periphery of the loop portion 14 of the core 12. A flexible reed 3 2 is fastened at one end 36 by appropriate means such as rivets 34 to one of the arms 28 of the bracket 22. The flexible reed 32 extends across the periphery of the core and terminates at its other end 37 adjacent the other arm 30 of the U-shaped bracket to form an air gap therewith. The center of the flexible reed 32 lies proximate to the periphery of the core 12 so as to form an air gap in the alternate magnetic flux path as hereinafter described. The device is maintained in assembly by a core casing 38 in the normal manner.

This transformenbuzzer device 10 operates in a manner such that when the leads 30 to the primary winding 18 are connected to a power source and the leads 42 of the secondary 20 are connected to a normal low load, the flux path through the core 12 will be essentially as shown by the arrows 44 in FIG. 3. However, when a large load is connected across the secondary winding leads 42 the high currents generated in the secondary winding 20 produce a large opposing magnetic flux which affectsthe reluctance of the center leg 16 of the core embraced by the secondary winding. The flux generated by the primary source currents will, therefore, be caused to take an auxiliary path as indicated by the arrows 48 in FIG. 2 extending from the periphery of the loop portion of the core through the air gap to the center of the vibrating reed 32 where it divides to flow to the opposite ends thereof and to the arms 28 and 30 of the U-shaped bracket, returning to the core at the center leg 16 between the primary and secondary windings and continuing around the loop portion 14 of the core.

It is to be understood that since the device operates on alternating current the direction of the arrows represent the direction of primary generated magnetic flux for only one-half cycle. During the other half of the cycle the magnetic flux is directed in the opposite direction and the fluctuations in the magnetic flux cause the flexible lead 32 to vibrate in accordance with the fluctuations to produce a buzzing noise as the reed strikes the arm 30 and/or the periphery of the magnetic core 12. It is to be understood that the foregoing description of the operation of the device is based on theoretical considerations which are not fully confirmable by presently known laboratory methods. It is, therefore, the intention of the applicant not to be bound by the above description of the operation.

Referring now to FIG. 1, there is shown a transformer buzzer device having its secondary connected to a temperature indicating system. The circuit shown has been schematically simplified and reference is made to the aformen-tioned application of Marshall Miles for a more detailed circuit description. This circuit comprises a thermistor 50 connected in series With a heater winding 52 for a bi-metal element 54. The series connected thermistor and heater winding are connected across the secondary winding 18 of the transformer buzzer device so that the heat supplied to the metal element 34 by the heater element 52 is governed by the temperature to which the thermistor S is subjected. The resistance of the thermistor has a negative temperature coeflicien-t so that, as the temperature to which it is subjected increases its resistance decreases, causing an increase in current flow through the heater element 52.

The bi-metal element 54 has a contact 56 thereon which is engageable with a second contact 58 so as to complete a short circuit through the contacts 58, 56 and the bi-metal element 54 directly across the secondary winding 18 of the trans-former buzzer. Therefore, when the temperature of the thermistor S0 is such that the bimetal 54 closes the contacts 56-58, the secondary winding will be short circuited to act as an extremely high load to the transformer buzzer. The magnetic flux condition as described with respect to FIG. 2 will result to provide an alarm that the temperature has been reached. It is to be noted that when the contacts 56, 58 close the thermistor 5i) and the heater winding 52 are effectively shunted and the bi-metal 54 will cool to cause the disengagement of the contacts 56, 58. Thus the device provides an intermittent alarm signal.

The temperature level at which the alarm indicating is to be given may be established by manually manipulating the distance between the contacts 56, 58.

The device herein described has great economic advantage-s in a competitive field because of its use of standard components in the core and the windings. It may also be seen that it is an easily assembled device which represents a great savings in its manufacture. The windings 18 and 20 and the U-shaped bracket 22 may be prefabricated and merely slipped onto the center leg 16 before completing the fabrication of the core 12. This is to be contrasted with the transformer-buzzer device shown in the aforementioned Miles application with the closed loop-type core requiring more expensive fabrication techniques.

While there has been shown one embodiment of a transforemer device it would be readily recognized by one skilled in the art that many modifications may be made thereto without deviating from the teachings of this invention. It is, therefore, intended to be bound not by the preceding description of the embodiment but only by the scope of the appended claims.

What is claimed is:

1. A combination transformer and buzzer device comprising a shell-type core having a loop portion and a center leg, a primary winding surrounding a portion of said center leg, a secondary winding surrounding another portion of said leg, a magnetic-fiux-permeable U-shaped bracket having an aperture centrally located in the base portion thereof securely receiving the center leg of said core between said primary and secondary coils, a magnetic-flux-permeable, flexible reed having one end fixed to the end of one of the arms of said U-shaped bracket having an aperture centrally located in the base the end of the other arm of said bracket, the middle portion of said reed lying adjacent said loop portion to define a second small air gap therewith.

2. A combination transformer and buzzer device comprising a shell-type core having a loop portion and a center leg, a primary winding surrounding a portion of said center leg, a secondary winding surrounding another portion of said leg, a magnetic-flux-permeable U-shaped bracket having an aperture centrally located in the base portion thereof securely receiving the center leg of said core between the adjacent ends of said primary and secondary coil-s, a magnetic flux-permeable, flexible reed having one end fixed to the end of one of the arms of said U-shaped bracket and the other end defining a small air gap with the end of the other arm of said bracket, the middle portion of said reed lying adjacent the perimeter of said loop port-ion proximate to the other end of said secondary winding to define a second small air gap with said core.

3. A combination transformer and buzzer device comprising a shell-type core having a loop portion and a center leg forming a main flux path, a primary winding surrounding a portion of said center leg, a secondary winding surrounding another portion of said leg, auxiliary magnetic flux means including a vibratable element with a variable air gap, said auxiliary flux path further comprising a structure extending from the outside of said center leg between said coils to said loop portion proximate to the junction between said loop portion and the end of said center leg adjacent the secondary winding.

4. A combination transformer and buzzer device comprising a shell-type core having a loop portion and a center leg forming a main flux path, a primary winding surrounding a portion of said center leg, a secondary winding surrounding another portion of said leg, auxiliary magnetic flux means including a vibratable element with a variable air gap, said auxiliary path further comprising a structure extending from the outside of said center leg between said windings to said loop portion of said core.

5. A combination transformer and buzzer device comprising a shell-type core having a loop portion and a center leg, a primary winding surrounding a portion of said center leg, a secondary winding surrounding another portion of said leg, a magnetic flux permeable bracket secured to said center leg between said primary and secondary coils, a magnetic-fiux-permeable flexible reed having one end fixed to said bracket and a portion thereof lying adjacent said loop portion to define a small air gap therewith.

References Cited by the Examiner UNITED STATES PATENTS 2,342,730 2/1944 Goodbar 340393 2,617,867 11/1952 Welch 340384 X 2,757,365 7/1956 Perez 34040*1 2,919,318 12/1959 Brown a"-.. 340233 NEIL C. READ, Primary Examiner. 

1. A COMBINATION TRANSFORMER AND BUZZER DEVICE COMPRISING A SHELL-TYPE CORE HAVING A LOOP PORTION AND A CENTER LEG, A PRIMARY WINDING SURROUNDING A PORTION OF SAID CENTER LEG, A SECONDARY WINDING SURROUNDING ANOTHER PORTION OF SAID LEG, A MAGNETIC-FLUX-PERMEABLE U-SHAPED BRACKET HAVING AN APERTURE CENTRALLY LOCATED IN THE BASE PORTION THEREOF SECURELY RECEIVING THE CENTER LEG OF SAID CORE BETWEEN SAID PRIMARY AND SECONDARY COILS, A MAGNETIC-FLUX-PERMEABLE, FLEXIBLE REED HAVING ONE END FIXED TO THE END OF ONE OF THE ARMS OF SAID U-SHAPED BRACKET HAVING AN APERTURE CENTRALLY LOCATED IN THE BASE THE END OF THE OTHER ARM OF SAID BRACKET, THE MIDDLE PORTION OF SAID REED LYING ADJACENT SAID LOOP PORTION TO DEFINE A SECOND SMALL AIR GAP THEREWITH. 